Photoconductive element containing furans, indoles, or thiophenes

ABSTRACT

Organic photoconductive elements of improved electrophotographic speed are prepared by coating on an electrically conducting support a photoconductive layer containing a 1,3diarylisobenzofuran or 1,3-diaryl-4,7-dihydroisobenzofuran or the corresponding isoindole or isobenzothiophene derivatives.

United States Patent [191 11] 3,784,376 F0X Jan. 8, 1974 PHOTOCONDUCTIVEELEMENT 3,174,854 3/1965 Stump t 252 501 CONTAINING FURANS, INDOLES, ORTHIOPHENES Charles J. Fox, Rochester, N.Y.

Eastman Kodak Company, Rochester, NY.

Filed: Feb. 4, 1972 Appl. No.: 223,770

Related US. Application Data Inventor:

Assignee:

US. Cl. 96/15, 252/501 Int. Cl G03g 5/00 Field of Search 96/15, 252/501References Cited UNITED STATES PATENTS 12/1969 Fox 96/].5

OTHER PUBLICATIONS C.A., v01. 57, p. 1743 1.

Primary ExaminerNorman G. T'orchin Assistant Examiner-John L. Goo drowAttorney-Robert W. Hampton et a].

Organic photoconductive elements of improved electrophotographic speedare prepared by coating on an electrically conducting support aphotoconductive layer containing a l,3-diarylisobenzofuran or 1,3-diaryl-4,7-dihydroisobenzofuran or the corresponding isoindole orisobenzothiophene derivatives.

ABSTRACT 10 Claims, No Drawings PHOTOCONDUCTIVE ELEMENT CONTAININGFURANS, INDOLES, OR TI-IIOPI-IENES This invention relates toelectrophotography and more particularly to novel organicphotoconductive materials.

Electrophotographic processes employ an electrophotographic orphotoconductive element comprising a coating of a photoconductiveinsulating material on a conductive support. The element is given auniform surface charge in the dark and then is exposed to an imagepattern of activating electromagnetic radiation such as light or X-rays.The charge on the photoconductive element is dissipated in theilluminated area to form an electrostatic charge pattern which is thende veloped by contact with an electroscopic marking material. Themarking material or toner, as it is also called, whether carried in aninsulating liquid or in the form of a dry powder, deposits on theexposed surface in accordance with either the charge pattern or thedischarge pattern, as desired. Then, if the photoconductive element isof the non-reusable type, the developed image is fixed by fusion orotherwise to the surface of the photoconductive element. If the elementis of the reusable type, e.g., a selenium-coated drum, the image istransferred to another surface such as paper and then fixed to provide acopy of the original.

All of this is well known and has been described in many patents andother literature, for example, in the patent of Carlson, U. S. Pat. No.2,297,691, and in more recent works such as Electrophotography by R. M.Scaffert, published by Focal Press Ltd., 1965.

It is also known that many organic materials can be used asphotoconductors. The organic photoconductors have a number of advantagesover the inorganic photoconductors such as zinc oxide, which arepresently more widely used. For instance, the organics are moreresistant to abrasion than the inorganics. They can be charged to eitherhigh negative or positive potential while the inorganics often saturateat low potential and are less versatile in that characteristically theyaccept only a positive or a negative charge. Also the organics usuallyoffer greater exposure latitude, can be spectrally sensitized moreeffectively and have other advantages over zinc oxide and otherinorganics.

These useful properties which organic photoconductors possess in greateror lesser degree have lead to a widespread interest in them. However,they also have certain disadvantages which render them less desirablethan zinc oxide for some uses. For example, many organic photoconductorshave low xerographic speed or sensitivity and those that have adequatespeed often have poor light stability and form colored materials byphotodegradation.

Among the many organic photoconductors that have been proposed arevarious 2,5-diarylfurans and 2,3- benzofurans, as disclosed, forexample, in German Pat. No. 1,105,714 and Belgian Pat. No. 585,450.Although these furan derivaties have a number of advantages as organicphotoconductors a problem has been that their sensitivity orelectrophotographic speed has not been as high as desired.

In accordance with the present invention I have discovered that certainisobenzofurans and related compounds have unexpectedly higherelectrophotographic speed than the furan derivaties which are reportedin the prior art as photoconductors and also have betterdiarylisobenzofura'n the 1 and 3 positions. The aryl groups can beseparated from the heterocyclic nucleus by conjugated linear car- CH CHwhere n=0 to 4. Therefore, in referring broadly to the 1,3-diarylsubstituted compounds herein, it is intended to include vinylogs inwhich one or both of the 1,3-aryl groupsis separated from theheterocyclic nucleus by one or more vinylene groups. The term aryl isthus used with respect to the 1,3- substituents to include not onlyphenyl, naphthyl and the like but also styryl, riaphthylvinylene and thelike.

Such compounds can be represented by the formulae:

and

wherein X is -O-, -S- or -NR; R is H or alkyl of 1 to 18 carbon atoms,preferably lower alkyl; Ar and Ar, are aryl groups; R,, R R and R, arehydrogen atoms or substituents, and n and m are integers from 0 to 4. Assubstituens, R R R and R, can be essentially any electropositive orelectronegative radicals such as alkyl, aryl, -COOR, -CONR -CN, halogen,-OR, -R'- COOR or -R-CONR,, wherein R is hydrogen or alkyl of l to 18carbon atoms and preferably is lower alkyl and R is an alkylene radicalof l to 18 carbon atoms, preferably lower alkyl (i.e., l to about 6carbon atoms). The aryl groups, Ar and Ar include, for example, phenyl,naphthyl, etc, and such radicals having substituents on the aromaticrings.

The photoconductive elements of the invention can employ any of thedescribed isobenzofuran and analogous compounds having the indicatedbroad range of substituents. Advantageously, however, compounds areemployed in which R R R and R and the values of n and m are such thatthe compounds are soluble in convenient solvents and are compatible withthe most effective binder resins. Best results in these respects areobtained when n and m are ml and R,, R R and R, are hydrogen atoms oralkyl groups of l to 18 carbon atoms, especially lower alkyl groups(i.e., 1 to about 6 carbon atoms).

Examples of the compounds of particular interest include the following:l,3-diphenylisobenzofuran; l,3- diphenyl-S,6-dimethylisobenzofuran;l,3-diphenyl-4,7- dihydroisobenzofuran; l-mesityl-3-phenylisobenzofuran; l,3-dimesitylisobenzofuran; 1,3-diphenyl-4,7-diethylisobenzofuran; 1,3-diphenyl-5,6-dimethyl-isobenzothiophene; l ,3-diphenyl-4,7- dimethylisoindole;l,3-bis(m-bromostyryl)isobenzothiophene;l,3-bis(p-dimethylaminostyryl)isobenzofuran;l-(2-naphthyl)-3-styryl-5,6- dimethylisobenzofuran; l,3-di(m-tolyl )-4-dimethylamino-7ethylisobenzothiophene; 1,3-bis-(4- phenyl-l,3-butadienyl-l )-2-methylisoindole; 1,3-bis- (Z-naphthylvinylene-l)isobenzofuran; 1,3-diphenyl-- methylisoindole;l,3-diphenyl-2-methylisoindole; 1,3- diphenyl-S,6-dimethyl-4,7-dihydroisobenzothiophene andl,3-diphenyl-2-methyl-4,7-dihydroisoindole.

lsobenzofurans and dihydroisobenzofurans of the types suitable in thecompositions of the invention and methods of preparing such compoundsare described, for example, by M. S. Newman, J. Org. Chem., 26, 2630(1960) and by Adams et al., J. Am. Chem. Soc., 62, 56 (1940). Theisobenzothiophene and isoindole compounds, i.e., where X in the formulaeabove is -S- or -NH-, can be prepared, for example, by the procedure ofMann et al., Chem. Commun. 1969, 420.

When employed as photoconductors in accordance with the presentinvention these compounds are mixed in an amount of l to 75 parts byweight with 25 to 99 parts by weight of a polymeric binder and arecoated from a suitable solvent on a conducting support to provide thephotoconductive layer of the electrophotographic element.

Preferred binders for admixture with the photoconductive compounds inpreparing the photoconductive layers of the present invention includepolymers having fairly high dielectric strength which are goodelectrically insulating film-forming vehicles. Materials of this typeinclude styrene-butadiene copolymers; silicone resins; styrene-alkydresins; silicone-alkyd resins; soyaalkyd resins; poly(vinyl chloride);poly(vinylidene chloride); vinyl chloride-vinylidene chloridecopolymers; vinylidene chloride-acrylonitrile' copolymers; poly(vinylacetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals),such as poly(vinyl butyral); polyacrylic and methacrylic esters, such aspoly(- methyl methacrylate), poly(n-butyl methacrylate), poly(isobutylmethacrylate), etc.; polystyrene; nitrated polystyrene;polymethylstyrene; isobutylene polymers; polyesters, such ascopoly[ethylene-coalkylenebis(alkyleneoxyaryl)phenylenedicarboxylate],e.g., poly[ethylene-co-isopropylidene-2,2'bis-(ethyleneoxyphenyl)terephthalate]; phenolformaldehyde resins;ketone resins; polyamides; polycarbonates; polythiocarbonates;copolymers of vinyl haloarylates and vinyl acetate such aspoly(vinyl-mbromobenzoate-co vinyl acetate); waxes, chlorinatedpolyethylene, etc. Especially preferred are thermoplastic resins.Suitable resins are sold under such trademarks as Vitel PE-lOl, Cymac,Piccopale 100, Saran F-220, Lexan 145 and Geon 222. Also mixtures ofthese binders can be used.

The photoconductive compositions formed by blending a polymeric bindersuch as a polyester or polycarbonate with a monomeric organicphotoconductor of the type described are preferred embodiments of theinvention, because they provide a wide choice of binders and ratios ofbinder to photoconductor. It is well known, however, to usepolymerizable photoconductors that require no separate polymeric binder.It should be understood therefore that it is within the scope of thepresent invention to use species of the described photoconductors thatcontain the active nuclei depicted above but that are polymerizable andrequire no separate polymeric binder, although even in this event apolymer of the polymeric binder type can also be blended with thepolymeric photoconductor if desired.

The polymeric photoconductors are prepared by polymerizing monomerswhich contain the described photoconductive nuclei (i.e.,1,3-diarylisobenzofuran or l,3-diaryl-4,7-dihydroisobenzofuran orcorresponding isobenzothiophene or isoindole) and which arepolymerizable to form either addition or condensation polymers. Additionpolymers can be formed when the monomeric photoconductor contains one ormore vinylene groups as, for example, when n or m or both in l or IIabove is a positive integer of l to 4. The addition polymerization canbe carried out by known catalytic techniques for polymerization of vinylmonomers.

Condensation polymers can be formed when, for example, in formulae l andll, two or more of the substituents R, through R, are radicals thatcondense with other radicals to form esters, amides, urethanes,carbonates, etc. These include radicals such as -Ol-l, -COOl-l.-COOalkyl, -Nl-l and the like. Conventional catalytic procedures forforming such condensation polymers can be used. For example, if R, and Rare carboxyl groups the isobenzofuran compound can be reacted with aglycol such as ethylene glycol in the presence of a catalyst such as anoxide of tin or titanium to form a polyester. The preferred condensationpolymers are polycarbonates and polyurethanes and especially preferredare those formed from monomers l or II when R, and R are thepolymer-forming functional groups such as hydroxyl groups, n and m arezero, and the monomer is reacted with phosgene or a diisocyanate.

Solvents useful for preparing coating compositions with thephotoconductors of the present invention can include a wide variety oforganic solvents for the components of the coating composition. Forexample, benzene; toluene; acetone; 2-butanone; chlorinated hydrocarbonssuch as methylene chloride; ethylene chloride; and the like; others,such as tetrahydrofuran and the like, or mixtures of such solvents canadvantageously be employed in the practice of this invention.

sensitizing compounds usful with the photoconductive elements of thepresent invention can be selected from a wide variety of materials,including such materials as pyrylium dye salts including thiapyryliumdye salts and selenapyrylium dye salts disclosed in VanAllen et al. U.S. Pat. No. 3,250,615; fluorenes, such as 7,12-dioxo-l3-dibenzo(a,h)fluorene, 5,10-dioxo- 4a,l l-'diazabenzo(b)fluorene, 3,13-dioxo-7- oxadibenzo-(b,g)tluorene, and the like; aggregate-typesensitizers of the type described in Belgian Pat. No. 705,117 dated Apr.16, 1968; aromatic nitro com pounds of the kind described in U. S. Pat.No.

2,610,120; anthrones like those disclosed in U. S. Pat. 2,670,284;quinones, U. S. Pat. No. 2,670,286; benzophenones U. S. Pat. No.2,670,287; thiazoles U. S. Pat. No. 2,732,301; mineral acids; carboxylicacids, such as maleic acid, diand tri-chloroacetic acids, and salicyclicacid; sulfonic and phosphoric acids; and other electron acceptorcompounds as disclosed by l-l. l-Ioegl, J. Phys. Chem., 69, No. 3,755-766 (March, 1965), an

U. S. Pat. No. 3,232,755.

The amount of sensitizer that can be added to a photoconductor layer togive effective increases in speed can vary widely. The optimumconcentration will vary with the specific photoconductor and sensitizingcompound used. In general, substantial speed gains can be obtained wherean appropriatesensitizer is added in a concentration range from about0.0001 to about weight percent or more based on the weight of thecoating composition. Normally, sensitizers are added to the coatingcomposition in an amount of about 0.005 to about 5.0 percent by weightof the total coating composition.

Coating thicknesses of the photoconductive composition on a support canvary widely. Normally, a coating in the range of about In to about 500p.after drying is useful for the practice of this invention. The preferredrange of coating thickness is found to be in the range from about Sp. toabout 200p. after drying although useful results can be obtained outsideof this range.

Suitable supporting materials for the photoconductive layers of thepresent invention can include any of a wide variety of electricallyconducting supports, for example, various conducting papers; aluminumcoated paper; aluminum-paper laminates; metal foils such as aluminumfoil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc,brass, and galvanized plates; varpor deposited metal layers suchas'silver, nickel or aluminum on conventional film supports such ascellulose acetate, poly-(ethylene terephthalate), polystyrene and thelike conducting supports. An especially useful conducting support can beprepared by coating a support material such as poly(ethyleneterephthalate with a layer containing a semiconductor dispersed in aresin as described in U. S. Pat. No. 3,245,833 or vacuum de posited onthe support. Likewise, a suitable conducting coating can be preparedfrom the sodium salt of a carboxyester lactone of a malaicanhydride-vinyl acetate copolymer. .Such kinds of conducting layers andmethods for their optimum preparation and use are disclosed in U. S.Pat. Nos. 3,007,901; 3,245,833 and 3,267,807.

The electrophotographic elements of the invention are used for makingxerographic images in the follow- -ingmanner:.The electrophotographicelement is held in the dark and given a blanket electrostatic charge byplacing it under a corona discharge. This uniform charge is retained bythe photoconductive layer because the substantial dark insulatingproperty of the layer, i.e., the low conductivity of the layer in thedark. The electrostatic charge formedon the surface of thephotoconductive layer is then selectively dissipated from the surface ofthe layer by image-wise exposure to light by means of a conventionalexposure operation such as, for example, by a contact-printingtechnique, or by lens projection of an image, and the like, to therebyform a latent electrostatic image in the photoconductive layer. Exposingthe surface in this manner forms a pattern of electrostatic charge byvirtue of the 6 fact that light energy striking the photoconductorcauses the electrostatic charge in the light struck areas to beconducted away from the surface in proportion to the intensity of theillumination in a particular area.

The charge pattern produced by exposure is then developed or transferredto another surface and developed there, i.e., either the charged oruncharged areas rendered visible, by treatment with a medium comprisingelectrostatically responsive particles having optical density. Thedeveloping electrostatically responsive particles can be in the form ofadust, i.e., powder, or a pigment in a resinous carrier, i.e., toner. Apreferred method of applying such toner to a latent electrostaic imagefor solid area development is by the use of a magnetic brush. Methodsfor forming and using a magnetic brush toner applicator are described inthe following U. S. Pat. Nos: 2,786,439; 2,786,440; 2,786,441;2,811,465; 2,874,063; 2,984,163; 3,040,704; 3,117,884; and Reissue25,779. Liquid development of the latent electrostatic image may also beused. In liquid development, the developing particles are carried to theimage-bearing surface in an electrically insulating liquid carrier.Methods of development of this type are widely known and have beendescribed in the patent literature, for example, U. S. Pat. No.2,907,674 and in Australian Pat. No. 212,315. In dry developingprocesses, the most widely used method of obtaining a permanent recordis achieved by selecting a developing particle which has as one of itscomponents a low-melting resin. Heating the powder image then causes theresin to melt or fuse into or on the element. The powder is, therefore,caused to adhere permanently to the surface of the photoconductivelayer. In other cases, a transfer of the electrostatic charge imageformed on the photoconductive layer can be made to a second support suchas paper which would then become the final print after development andfusing. Techniques of the type indicated are well known in the art andhave been described in a number of U. S. and foreign patents, such as U.S. Pat. Nos. 2,297,691 and 2,551,582 and in RCA Review Vol. 15 (1954)pages 469-484.

The following example further illustrates the principles of theinvention.

EXAMPLE 1 Electrophotographic elements or plates are prepared in thefollowing manner: To a solution of 0.15 grams of the organicphotoconductive compound and 0.002 grams of a sensitizing dye in 5 ml.of methylene chloride is added 0.050 grams of Vitel PE-l0l* *Vitel PE-101 is a trademark of Goodyear Tire & Rubber Company for a copolyesterof terephthalic acid with a glycol mixture having a 9:1 molar ratio ofethylene glycol and 2,2-bis-(4-B-hydroxyethoxyphenyl) propane.polyester. The mixture is agitated to obtain a clear viscous solution ordope which is knife-coated on aluminum foil at about F. and a wetthickness of 0.004 inches. The coated product is dried anddark-conditioned by heating for fifteen hours in a dark oven at 47 C.Samples of the resulting xerographic element are charged in totaldarkness by means of a negative corona and then exposed through a steptablet to the light of a tungsten lamp at an illumination intensity ofabout 19 foot-candles for 12 seconds. The step tablet is of thecarbon-grain-in-gelatin type with density increments of 0.15. An inlayof 2.0 density covers one half of the tablet to extend the range ofexposure. A photographic film positive carrying printed text and numbersidentifying the steps lies between the photoconduetive layer and thetablet.

The resulting electrostatic latent image is developed by cascading overthe surface of the photoconduetive layer a mixture of negatively chargedthermoplastic toner particles and plastic beads.

Following the described procedure a series of electrophotographicelements is prepared using the furan compounds I through V andsensitizers (or no sensitizers) as indicated in the following lists offuran compounds and sensitizers and the table hereinafter. Elements arealso prepared which contain a furan compound but no sensitizer and acontrol element is prepared which contains only the polyester binderresin and the sensitizer B.

Furan Compounds 7 1 ,B-dlph enyllsobenzoiuran1,3-dlphenyl-5,G-dlmethyllsobenzofuran 1,3-rliphenyl-4,7dihydroisobenzoluran i 1,3,4,7-tetraphanyllsobenzofuran 2,6-dlpl1enylluranSENSITIZERS A. No sensitizer added.

B. 4-(4-n-amyloxyphenyl)-2,6-bis(4-ethylphenyl)- thiapyryliumperchlorate C. 2,4,7-trinitrofluorenone D. Crystal violet E. Rhodamine BF. 2,4-bis-(4-ethoxyphenyl)-6-(4-amyloxystyryl) pyrylium fluoroborateThe table below records the results of the described xerographicexposure of plates containing the organic photoconductors andsensitizers indicated in the table. (Except that the data for theelement containing compound IV are from a test with positive charging.in a negative charging test, which possibly failed for other reasons,the element containing this compound yielded no image). The speeddesignations in the table are relative speeds indicating the multiple bywhich the particular xerographic element is faster than the control thatcontains only the polyester binder resin and sensitizer B. With theprocedure described the control gives a detectable image to about step10.

Table Photoconductor Sensitizer image Formed Speed Rating I A (None) Yes24 l B Yes 200 l C Yes 48 l D Yes 98 l E Yes 200 II A (None) Ycs 78 ll EYes Ill C Yes 150 IV B Yes 57 IV C Yes 20 IV D No IV E Yes l5 V A (None)No V B Yes 38 V C Yes 6 V D No V E Yes 5 None A (None) No (Control) BYes 5 C No D No E No

The results recorded in the table show that the described isobenzofurancompounds I, II and III are photoconductors of good sensitivity. Theyare unexpectedly superior to a simple diaryl substituted furan such ascompound V. in these particular comparisons compound lV,(1,3,4,7-tetraphenyl-isobenzofuran, which is also a1,3-diarylisobenzofuran of the type contemplated herein) is not asmarkedly. superior to photoconductor V and the control element as arecompounds I, ll and Ill. An explanation for these results which are notas good as can be obtained with compound IV is that some crystallizationof the compound occurred in this particular coating. The followingexample describes a coating in which substantially better results areobtained with compound lV.

EXAMPLE 2 The crystallization of the 1,3,4,7-tetraphenylisobenzo-furanencountered in Example 1 is eliminated or reduced in a photoconduetiveelement prepared substantially as in Example 1 but using bisphenol-Apolycarbonate (Lexan polycarbonate) as the binder instead of polyesterand using approximately 15 percent concentration of the compound in thecoating instead of approximately 20 percent. Testing of suchcompositions containing compound IV and either sensitizer B 9 orsensitizer F for positive and negative charging gives the followingresults:

- speed Photoconductor Sensitizer Positive Negative IV E I 71 IV F 170160 The next example illustrates the use of the following thiobenzofuranand isoindole compounds in photoconductive elements of the invention:

' asbestosis. 6551501155 1,2,3-triph enylisoindole EXAMPLE 3Photoconductive elements of the invention containing a thiobenzofuran(compound VI) or an isoindole (compound VII) are prepared as in Example1, using the following basic formulation:

Photoconductor 0.25 g.

Vitel 101 polyester 1.00 g.

Sensitizer 0.01 g.

Methylene chloride 9.60 g.

Results obtained with these compositions positively charged and testedas in Example 1 are as follows:

Photoconductor Senlitizer Image Formed Speed Rating Vl B Yes 200 E YesI00 VII B Yes 50 E Yes 50 Compounds of somewhat related structure whichappear to have some utility as organic photoconductors, although nothaving the surprisingly high sensitivity of thel,3-diarylisobenzofurans, include the following isoindoles:l-(4-dimethyl-amin0phenylisoindole, 1 phenylisoindole andl-(4-methoxyphenyl) isoindole.

The invention has been described in detail with particular reference topreferred embodiments thereof,

but it will be understood that variations and modifications can beeffected within the spirit and scope of the invention.

I claim:

1. A photoconductive element comprising an electrically conductingsupport and having thereon a layer comprising a polymeric binder with anorganic photoconductive compound of the formula where R R R and R arehydrogen, alkyl, aryl,

-COOR, -CON(R) CN, halogen, -OR, -R'-COOR, or

-R'-CON(R) wherein R is hydrogen or alkyl and R is an alkylene radical;Ar and Ar, are aryl groups; X is O, S, or NR; and n and m are integersfrom 0 to 4.

2. An element according to claim 1 in which R R R and R are hydrogen orlower alkyl.

3. An element according to claim 2 in which a sensitizing dye isincorporated with the organic photoconductor compound.

4. An element according to claim 3 in which the organic photoconductorcompound is 1 ,3- diphenylisobenzofuran.

5. An element according to claim 3 in which the organic photoconductorcompound is l,3-diphenyl-5,6- dimethylisobenzofuran.

6. An element according to claim 3 in which the organic photoconductorcompound is l,3-dipheny1-4,7- dihydroisobenzofuran.

7. An element according to claim 1 comprising a photoconductive layercoated on an electrically conducting support, said layer comprising (a)a photoconductive compound selected from the group consisting ofl,3-diphenylisobenzo-furan, l,3-diphenyl-5,6- dimethylisobenzofuran andl,3diphenyl-4,7- dihydroisobenzofuran, (b) a sensitizing dye and (c) apolymeric binder.

8. An element according to claim 7 in which the polymeric binder is amajor component of the photoconductive layer and is a terephthalicpolyester.

9. An element according to claim 7 in which the polymeric binder is amajor component of the photoconductive layer and is a bisphenoLA.polycarbonate.

10. An element according to claim 3 in which the organic photoconductorcompound is l,2,3-

triphenylisoindole.

2. An element according to claim 1 in which R1, R2, R3 and R4 arehydrogen or lower alkyl.
 3. An element according to claim 2 in which asensitizing dye is incorporated with the organic photoconductorcompound.
 4. An element according to claim 3 in which the organicphotoconductor compound is 1,3-diphenylisobenzofuran.
 5. An elementaccording to claim 3 in which the organic photoconductor compound is1,3-diphenyl-5,6-dimethylisobenzofuran.
 6. An element according to claim3 in which the organic photoconductor compound is1,3-diphenyl-4,7-dihydroisobenzofuran.
 7. An element according to claim1 comprising a photoconductive layer coated on an electricallyconducting support, said layer comprising (a) a photoconductive compoundselected from the group consisting of 1,3-diphenylisobenzo-furan,1,3-diphenyl-5,6-dimethylisobenzofuran and1,3-diphenyl-4,7-dihydroisobenzofuran, (b) a sensitizing dye and (c) apolymeric binder.
 8. An element according to claim 7 in which thepolymeric binder is a major component of the photoconductive layer andis a terephthalic polyester.
 9. An element according to claim 7 in whichthe polymeric binder is a major component of the photoconductive layerand is a bisphenol-A polycarbonate.
 10. An element according to claim 3in which the organic photoconductor compound is1,2,3-triphenylisoindole.